1. Field of the Invention
The present invention relates to a vehicle communication apparatus for performing radio communication between vehicles on roads and a system for supporting vehicles, namely, drivers on the vehicles which pass through a narrow road, and in particular, relates to the vehicle communication apparatus and the system that are incorporated in a car navigation system mounted on each vehicle.
2. Description of the Related Art
Recently, there have been reported many techniques using a vehicle communication apparatus. For example, there are three prior art documents that have disclosed following techniques, in Japanese patent laid open publications (a) JP2000-276696, (b) JP-H11-83508, and (c) JP2004-245610. Such a conventional vehicle communication apparatus assists the vehicle to communicate with other vehicles.
The prior art document (a) JP2000-276696 has disclosed a vehicle collision evading control apparatus. The apparatus is capable of receiving position data of an on-coming vehicle and possibility data of the presence of the on-coming vehicle. The apparatus then calculates a possibility of collision and time and a position of the predicted collision between the driver's vehicle and the on-coming vehicle based on the received data. Further, the apparatus informs those predicted data items to the driver of the vehicle in order to avoid the vehicle collision.
The prior art document (b) JP-H11-83508 has disclosed a car navigation system. The apparatus is equipped with a radio communication means or a radar detection means capable of detecting an on-coming vehicle on a narrow road such as a mountain path. Those means then calculate a predicted point on the narrow road on which own vehicle and the on-coming vehicles are passing through each other. The radio communication means then informs the predicted point to both the drivers of its own vehicle and the on-coming vehicle.
The prior art document (c) JP2004-245610 has disclosed a car navigation system capable of detecting a presence of an on-coming vehicle using a vehicle communication apparatus for communicating with vehicles. The apparatus detects the presence of an on-coming vehicle traveling in a narrow area on a road where both vehicles cannot pass through each other when one vehicle approaches within a given distance measured from the narrow area on the road or when one vehicle is traveling on the narrow area. The apparatus calculates and then informs an optimum predicted point where the vehicle and the on-coming vehicle would be passing through each other.
FIG. 9A shows a road map where there are a wide road 2A having double traffic lanes, a narrow road 1a of a single traffic lane, and a wide road 2B having double traffic lanes. The narrow road 1a is a road where it is difficult for opposing vehicles to pass through each other and only a single vehicle can pass through it. Each of the wide roads 2A and 2B is a road where it is easy for opposing vehicles to pass through each other.
When a vehicle A that stops on the wide road 2A near the narrow road 1a and travels to the wide road 2B through the narrow load 1a, the vehicle A must be wait for a long time period until the tail vehicle E in the on-coming vehicles B to E passes through the narrow road 1a. In this case, even if using the conventional communication apparatus described above, although the vehicle A can recognize the position and running state of the vehicles B to E, it is impossible to solve the problem in which the vehicle A must be wait at the point on the wide road 2A near the narrow road 1a until the tail vehicle E passes through the narrow road 1a completely.
For example, the stop vehicle A transmits a request to stop the on-coming vehicles D and E on the wide road 2B near the narrow road 1a. Even if the vehicle A on the wide road 2A receives information regarding the stop of the vehicles D and E on the wide road 2B according to the request transferred from the vehicle A and thereby recognizes that the vehicles D and E stop on the wide road 2B, the vehicle A can not approach to and pass through the narrow 1a and the wide road 2B until the vehicles B and C have passed through the narrow road 1a. The vehicle can thereby pass through the narrow road 1a without waiting until the tail vehicle E passes through the narrow road 1a. 
However, in the case shown in FIG. 9B where plural on-coming vehicles B to H travel in train on the narrow road 1a and the wide road 2B, there causes various problems such as a communication channel shortage or radio interference. The communication channel shortage means the lacking of the number of channels in radio communication. When those problems occur, the vehicle A can communicate with only some of the on-coming vehicles, for example, with the vehicle B and the vehicle E, but cannot communicate to all of the on-coming vehicles B to H. In this case, the vehicle A can not communicate with the on-coming vehicles G and E in order to send the request to stop the on-coming vehicles G and H. Further, a display device incorporated in the vehicle A cannot display the presence of the vehicles G and H traveling on the wide road 2B. That is, the display device on the vehicle A displays only the positions of the on-coming vehicles B to E and own vehicle A, but cannot display the presence of the vehicles g and H, as shown in FIG. 8C.